Photosensitive lithographic printing plate precursors comprising a non-silver photosensitive layer such as a photosensitive layer comprising an o-quinonediazide compound provided on a support having a hydrophilic surface such as an aluminum plate and a gelatino silver halide photosensitive emulsion layer provided on the layer are described in, for example, British Pat. No. 1,227,603. The plate making process for producing lithographic printing plates from such photosensitive lithographic printing plate precursors comprises the steps of (a) imagewise exposing to light the gelatino silver halide photosensitive emulsion layer and (b) developing it to form a silver image, (c) uniformly exposing to light the non-silver photosensitive layer masked by the silver image formed, (d) removing the silver image-containing layer (namely, the gelatino silver halide photosensitive emulsion layer imagewise exposed to light and developed) by washing out, and (e) developing the non-silver photosensitive layer.
In this plate making process, it is necessary for the silver image formed in the above-described step (b) to be firmly adhered to the non-silver photosensitive layer to serve as a mask until the uniform exposure step (c) is concluded and for it to be easily removed from the non-silver photosensitive layer in the wash-out step (d).
However, in the prior photosensitive lithographic printing plate precursors, there was the disadvantage that the gelatino silver halide photosensitive emulsion layer easily dissolved in the development step (b). Particularly, in processing using a roller conveyor type automatic plate making machine, a serious disadvantage existed in that the gelatino silver halide photosensitive emulsion layer was damaged or separated from the non-silver photosensitive layer when such was passed through rolls in the development zone and it did not sufficiently serve as a mask in the subsequent uniform exposure step (c), by which a desired lithographic printing plate could not be obtained.